Thus far, in response to the size reduction of an electronic device, electrical device, and the like, there have been attempts to reduce the size and thickness of components for electronic and electrical devices such as a terminal such as a connector, a relay, and a lead frame which are used in the electronic devices or the electrical devices. Therefore, as a material constituting components for electronic and electrical devices, there has been a demand for a copper alloy having excellent properties, strength, and bendability. Particularly, as described in NPL 1, a copper alloy which is used for components for electronic and electrical devices such as a terminal such as a connector, a relay, and a lead frame desirably has a high proof strength.
As a copper alloy that is used for components for electronic and electrical devices such as a terminal such as a connector, a relay, and a lead frame, the Cu—Mg alloy described in NPL 2, the Cu—Mg—Zn—B alloy described in PTL 1, and the like have been developed.
As is clear from the phase diagram of a Cu—Mg system illustrated in FIG. 1, in the Cu—Mg-based alloy, in a case in which the content of Mg is 1.3% by mass or higher (3.3% by atom or higher), an intermetallic compound made up of Cu and Mg can be precipitated by performing a solution treatment and a precipitation treatment. That is, in the Cu—Mg-based alloy, it becomes possible to obtain relatively high conductivity and strength by means of precipitation hardening.
However, in the Cu—Mg-based alloy described in NPL 2 and PTL 1, since there are many coarse intermetallic compounds, which include Cu and Mg as major components, dispersed in the matrix, cracking and the like are likely to occur from this intermetallic compound, which serves as a starting point during bending working, and thus there has been a problem in that a component for electronic and electrical devices having a complicated shape cannot be metal-formed.
Particularly, in components for electronic and electrical devices which are used for commercial products such as a mobile phone and a personal computer, there is a demand for a reduction of size and weight, and a copper alloy for electronic and electrical devices satisfying both strength and bendability is required. However, in a precipitation-hardened alloy such as the above-described Cu—Mg-based alloy, when strength and proof strength are improved by means of precipitation hardening, bendability significantly degrades. Therefore, it has been impossible to shape a thin component for electronic and electrical devices having a complicated shape.
Therefore, in PTL 2, a work-hardened copper alloy of a Cu—Mg supersaturated solid solution produced by quenching a Cu—Mg alloy after formation of a solid solution thereof is proposed.
Such a Cu—Mg alloy has excellent strength, conductivity, and bendability in a balanced manner and is particularly suitable as a material for the above-described components for electronic and electrical devices.